This application relates generally to steering columns and more particularly to a reactive energy absorbing system for a steering column.
Many steering column assemblies today are equipped with kinetic energy absorption devices to reduce the likelihood of injury in case of an accident. Such devices come in many different forms. One form that is particularly effective in absorbing significant quantities of energy in a relatively small amount of space employs a plastically deformable member such as a metal strap which is bent over an anvil or bushing. In the event of a head-on collision, the deformable strap is drawn across the anvil or bushing and the deformed shape travels along the length of the strap, causing a reaction force resisting collapse of the steering column and absorbing energy.
Typically energy absorbing devices, such as those employing a plastically deformable strap, are designed to protect drivers of average weight in a collision of average severity, without taking into account the fact that all drivers are not of average weight and that collisions vary considerably in severity depending on vehicle speed at the time of the impact.
In accordance with the present invention, it is possible to vary the reaction force resisting collapse of the steering column. For example, the energy absorbing device of this invention may provide a smaller amount of resistance in the case of a less severe collision or a lower weight driver, or a greater amount of resistance in the case of a more severe collision or a driver of greater weight.
More specifically, the energy absorbing device of this invention includes first and second elongated plastically deformable straps connected to a steering column, and a bushing connected to stationary vehicle support structure, or vice versa. The bushing interacts with the straps in a manner such that when the steering column collapses the straps advance linearly over the bushing and resist collapse of the steering column. One of the straps may be disconnected from the steering column at the instant of a crash event, in circumstances where less resistance to steering column collapse is desired.
In accordance with a preferred embodiment of the invention, the straps are generally U-shaped and wrap around the bushing. One of the straps is connected to the vehicle support structure by a retractable pin. The pin is retracted by an actuator which is operable by a signal generated by a controller in response to a vehicle collision. The controller, after monitoring such factors as driver weight, driver position, whether or not the driver is belted, and the intensity of the collision, may or may not call for retraction of the pin and release of one of the straps. If the controller determines that both straps are needed to resist collapse of the steering column, no signal will be sent to the actuator and hence both straps will be involved in the resistance to steering column collapse. If a lesser amount of resistance to the collapse of the steering column is indicated, the controller will send the appropriate signal to the actuator calling for the retraction of the pin and the release of one of the straps. The actuator may if desired be in the form of a fast-acting pyrotechnic device.
In another modification of the invention, a tear strip may be interposed between the straps, the tear strip being connected to each strap by a line of severance. The bushing is connected to the tear strip so that when the straps advance linearly over the bushing the straps tear away and separate from the tear strip along the two lines of severance. Here again, one of the straps may be disconnected where less absorption of energy is desired.
One object of this invention is to provide an energy absorbing device having the foregoing features and capabilities.
Other objects, features and advantages of the invention will become more apparent as this description proceeds.